Rotatable waveguide joint



Jan. 9, 1962 A. ALFORD ET AL ROTATABLE WAVEGUIDE JOINT Filed July 26, 1957 N\ mm r IN h l) INVENTORs wm) Lfop BY .PW/ H00?. Eze/w1. Non? Jan. 9, 1962 A. ALFORD ET AL 3,016,504

ROTATABLE WAVEGUIDE JOINT Filed'July 26, 195'? 2 Sheets-Sheet 2 .over a frequency ratio of l.-5 :1.

United States Patent 3,016,504 ROTATABLE WAVEGUIDE JOINT Andrew Alford, Winchester, and David P. Flood, Natick, Mass. (both of 299 Atlantic Ave., Boston, Mass.) yliiled July 26, 1957, Ser. No. 674,394 5 Claims. (Cl. 333-98) The present Iinvention `.relates to a rotatable waveguide joint and vmore particularly to a rotatable waveguide -joint .employing coaxially aligned fand facing transforming -horns.4

Attempts vhave been made in the ypast to design rotary waveguide joints for transmission of R.F. signals over .very side bands. Some of these attempts have utilized ifacing `circularly polarized horns in a manner such as Xdisclosed in United States Patent No. 2,535,251, issued December 26, 1950. While such structures were designed for broad band Y transmission and in fact make statements to such effect, `the band of transmission is less than 1.5:1 -and .does in yfact transmit such `a narrow band that it lmust ibe truly classied as a narrow band transmitting device.

A-further examination of the prior art indicates that all "of these so-called -broad -band rotary joints work over :frequency ,of the .order of 1.1 or sometimes as high as 1.321, in terms of theratio of the higher frequency to the *lower frequency. No rotary joint vis known that works Experimentation has 'proved that while a lrotary -joint may be made to work over a frequency ratio of 1.5:1 in a waveguide to coaxial line and coaxial line .to waveguide structure, such a structure is diicult to design and build for a proper and consistent operation.

Thus, .the present invention -provides a simplified rotary joint involving waveguide and horn transmission elements. In this arrangement, a pair of vvery broad band circularly polarized horns are pointed into one another with the .horns coaxial and Yaxially rotatable with respect to one another. These horns are each of a particular design for elfecting a circular polarization, with additional means .provided for absorbing a-portion of the iield, which it `has been `foundvin the absence of such means caused resonant conditions vwithin the bandof transmission.

An object, therefore, of the present invention is to pro- -vide a -rotary waveguide ljoint capable o-f transmitting wide bands of frequency with minimum attenuation in the joint.

Another object of the invention is to provide a structure which is simplived in design and which Vwill effective- -ly operate with assured certainty.

' These and other objects of the invention will be more clearly understood when considered in conjunction ,with the accompanying drawings in which:

FIGURE 1 isa part-iallyfcross-section Vplan viewof the rotary j oint transmission assembly ywith supporting structure and connecting wide waveguides omitted,

FIGURE 2 is a perspective vview .of the rotary joint spear assembly,

3,016,504 Patented J am ,9., ,195.2

FIGURE l2 illustrates the orientation of E vectors of transmitted and reflected waves at the rectangular opening of flange 5.

The individual horns which comprises this `rotary joint are in some respects similar to co-pending application Serial No. 5110.882, med May 2S, 1.955., ,in the aan@ Q f Andrew Alford for Horn for Radiating Circnlarly Polarized Waves, of which the present casemay be considered a continuation-in-part.

Referring to the figures, there are illustrated two transmission assemblies 1 and 2, each being somewhat similar -in structure to the other. These structures maybe iixed and secured within a tubular supporting structure (not shown) with one transmission assembly iixed ata spaced distance from and in axial alignment with Vthe other. Transmission assembly 1 (for example) may be supported for coaxially aligned Yrotation with -respect to assembly 2. The adjacent portions of these assemblies may be spaced apart from a few thousandths of an inch to `oneeighth of an inch or more, the distance between these assemblies not being very critical although `a close spacing is preferable yto avoid attenuation at the joint. The outer ends of the adjacent assemblies may be suitably connected to waveguides (not shown) for receipt and transmission of propagated wave energy. Thus, the device herein illus- -trated may be Vused for many purposes, as 'for example, it may be used for transmitting R.F. energy to a l.rotating antenna over a wide frequency band. yIn'such a, structure a 'servo-mechanism may be suitably connected `to `the -antenna for rotating it and the lattached transmission iassembly with respect to the other assembly.

Transmission assembly 1 comprises a waveguide tion 3 and a horn 4 coaxially aligned and inter-engaged at adjacent ends, with a flange 5 positioned at the `op- -posite end of waveguide section 3 and formed with a rectangular opening adapted for connection to a mating rrectangular waveguide. y,Waveguide.section 3 has a s qnare cross-sectioned portion V6 at the end adjacent `the horn.

.From substantially a center circumferential line 7 lthe waveguide 3 Viiares outwardly to the right to the flange 5 in a portion 8 having an octagonal cross-section. portion 8 is formed of a series of isoceles Atriangles with alternate triangles having their vertices coincident with the corner edges ofthe waveguide portion 6. The corners of the base of these last mentioned isosoeles triangles and the vertices of the intermediate triangles -are each aligned coincident v`with planes passing `longitudinally through -the center and .normal to the side walls vforming the waveguide portion 6. This portion 8 .is suitably secured to the ange 5 which is flared outwardly .and which has Aa center rectangular opening coincident with .the periphery of the portion 8 at the right end thereof, portion -8 providing a transition yfrom the square .cross :section in portion y6 to the .rectangular cross section .of the opening in fiange 5. The ange 5 may be of heavier metal than Athe waveguide section -3 fas is illustrated. Extending from the left of the transmission assembly-:1 is the horn v4 which comprises essentially va cylindrical lsection 10 having an outwardly extending `ange Arrnenrber 11 formed `with a shoulder section V12 about the periphery of the flange 1,1. `An axial opening 13 has a Y diameter substantially equal to the inside diagonal dimension of waveguide section 3 at the right end thereof. This opening 13 may be tapered toward the ,waveguide vsection f3 as indicated at 14 yfor fitting lthe inner configuration to vthe flared annular portion 15. Coaxial Iwith the horn 4 and waveguide section 3 is a spear assembly generally indicated at 16 and best illustrated in FIGURE 2. 'This spear assembly v16 extends axially and longitudinally through i -the transmission assembly 1 from -the .flange z5 =to the center of the .horn 4. 'Il-his spear is quite similar `.inconstruction to that shown in application Serial No. 510,882 and operates in conjunction with waveguide section 3 for transmission of the TElo and TEM modes through the transmission assembly in a manner similar to that described in that case. This spear 16 is formed with a at tongnle 26 at the left end (see FIGURE 8), the flat tongue 26 becoming slightly thicker and having two pairs of side walls 27 and 28, one pair on either side of the tongues which becomes wider as the thickness of the spear increases until at the section 9--9 it appears as shown in FIGURE 9 with the side walls 27 and 28 larger and with the thickness of the spear increased. The side walls 27 and 28 gradually are transformed as shown in FIGURES l and ll until the section of the spear becomes rectangular with the adjoining walls coming to a point as indicated at 29, so that the transformation of the spear begins with a flat tongue and goes through a sixsided figure gradually emerging at the right end of the spear in the shape as shown in FIGURE 4. The spear, as indicated, is supported within the square waveguide by opposite dielectric fins or plates. These opposite dielectric tins or plates are indicated in FIGURES 2 and 3 as 31, 32, 33 and 34. At the left end termination of the transmission portion 8 the two modes of propagation TEm and TEM are fully and completely established and some retardation has been effected on TEN by the extension of the dielectric elements 31 and 33 into this section, comprising the end sections 40 and 41 of these supporting dielectric elements respectively, which are shown in FIGURE 2, as iin-like in elfect, and formed with the two sides inclined towards one another coming together at a point somewhere towards the middle of the portion 8. This retardation of TEM, mode is continued through the portion 6 of the transmission assembly 1 by means of dielectric supporting plates or ns 31, 33 and 32, 34 which extend longitudinally with but in a plane normal to each other. These two pairs of plates or fins serve the two purposes of supporting and locating the spear within the assembly and also for the purpose of effecting the proper retardation through the horn so that the T1310 mode and TEM mode at the outlet of the horn in the mouth 13 provides a circularly polarized mode of propagation. The spear at the right end of the horn is terminated in a slightly decreasing square section 52 and then just within the end of the horn is tapered off to a point as indicated at 53.

The propagation of the wave from the input waveguide through the transmission assembly 1 is similar to that described in application Serial No. 510,882 with the wave propagated being converted into both TEN and TEM modes by the transition section. The theory of operation is fully described in that case. However, it is believed that the waves propagated are not truly circularly polarized waves but rather are elliptically polarized waves. In support of this theory it has been found that the structure as hereinbefore described does not always work at all frequencies. At a number of frequencies within what would be the frequency range of the rotary joint, there are Very well marked resonant conditions which result in substantial losses of the signal transmitted through the joint. In order to observe one of these resonant conditions, it is necessary only to rotate one member of the joint with respect to the other and to observe the signal transmitted through the joint. At some frequencies at two specic angles differing 180 from each other, the joints introduce substantial attenuation. It is theorized that the normal mode transmitted through the waveguide has its electric field normal to the long cross-section dimension of the rectangular opening in flange 5. This will not be reected in the transmission assembly if absorbed by a proper load.

A mode normal to the last mentioned mode and having its electric eld parallel to the long cross-section dimension of the latter rectangular opening is below cutoff and consequently will be reilected back. The orientation of electric vectors for transmitted and reflected waves in the rectangular opening of ange 5 is shown in FIG. 12. It is transformed into a circularly polarized wave having a eld of opposite rotation to the field created by the normal mode. Thus when it reaches the horn of the other transmission assembly it will again be reilected back causing a resonant condition at selected frequencies as indicated above.

In order to eliminate resonant conditions existing at specific frequencies and different relative positions of rotation, a pair of wave-absorbers 71 and 72 are secured to the spear 16. These wave-absorbers 71 and 72 each consists of a pair of thin butterfly-shaped lossy means 73 and 74. Each of these elements 73 and 74 may comprise a Bakelite sheet coated with carbon on one side. They are positioned between the spear and the inner surface of the waveguide in the portion 8 towards the rear of the spear. These waveguide absorbers are positioned parallel to the orientation of the electric vector of the reflected wave for absorbing the reflected energy while negligibly attenuating the transmitted wave whose electric vector is orthogonal to the plane of elements 73 and 74. A dielectric spacing pin projects between each pair of wave-absorbers 73 and 74 and properly spaces the end of the spear from the waveguide section 3. These pins 80 are adjustably secured by retaining screws 81 fitting into annular internally threaded members 82. The retaining screws 81 are provided with an O-ring 83 between the screw and member 82. The shape of the wave-absorbers 73 and 74 may be varied. However, the butterfly-shape described above is preferable. These wave-absorbers are designed to absorb reected standing waves. For this purpose the absorbers should be sufliciently long to be within the maximum points of the standing Wave.

In furtherance of assuring efficient absorption, the absorbers should be positioned in each transmission assembly at different relative longitudinal positions with the shapes, if desired, different for the absorbers in each assembly.

In the transmission assembly 1 a male annular ring and a female ring 91 with an intermediate annular ring 92 having a V-shaped cross-section are retained in the shoulder section 12 by the retaining plate 93, suitably secured by screws or the like to the flange 11. This assembly provides a friction surface on the ring 92 for rotation of the transmission assembly 1 with respect to the transmission assembly 2. The ring 92 provides a friction contact with the inner surface of the supporting member.

The transmission assembly 2 is similar in construction Vto the transmissionassembly 1, with the exception that the flange 95 is provided with an annular recess 96 within which there is positioned an O-ring 97 which seals this transmission assembly at the junction of the ilange 95 and the supporting structure. There is also provided in this flange arrangement an annular recess 98 spaced approximately one-fourth of a wave-length of the mean operating frequency from the inner wall of the horn. This recess should also have a depth of a quarter of a wave-length of the mean operating frequency. This arrangement provides a choke which acts to minimize the attenuation of propagated waves through the space between the facing anges.

We claim: Y

1. A rotary waveguide joint comprising, a pair of transmission assemblies each having a horn closely adjacent to and facing the horn of the other assembly for exchanging circularly polarized energy therebetween within a prescribed frequency range, said horn being coupled to a guide section formed with a rectangular opening at one end coupled to a portion of square cross section by a transition section, the dimensions of said rectangular opening being selected to correspond to those of a rectangular waveguide capable of supporting the propagation of energy within said prescribed range having its electric vector parallel to the narrow dimension of said opening while suppressing the propagation of microwave energy within said prescribed range having its electric vector parallel to the wide dimension of said opening, said portion of square cross section being dimensioned to support the propagation of both TEM, and TEO, modes of energy within said frequency range, a metallic insert within said guide section spaced from the walls thereof by dielectric delay means arranged to impart a relative delay between the TEM, and T E01 modes of substantially 90 electrical degrees within said prescribed frequency range, and means between said dielectric delay means and at least one of said rectangular openings for absorbing energy traveling from said horn toward said rectangular opening which would arrive thereat with its electric vector oriented generally parallel to said wide dimension while negligibly attenuating microwave energy travelling in the same direction and arriving at said opening with its electric vector oriented generally parallel to said narrow dimension.

2. Apparatus for transmitting circularly polarized microwave energy of a predetermined rotation over a prescribed frequency range comprising, a horn for receiving circularly polarized energy, a guide section formed with a rectangular opening at one end coupled to a portion of square cross section by a transition section to transfer energy between said horn and said opening, the dimensions of said rectangular opening being selected to correspond to those of a rectangular waveguide capable of supporting the propagation of microwave energy within said prescribed range having its electric vector parallel to the narrow dimension of said opening while suppressing propagation of microwave energy within said prescribed range having its electric vector parallel to the wide di-k mension of said opening, said portion of square cross section being dimensioned to support the propagation of both TEM, and TEol modes of microwave energy within said frequency range, `a metallic insert within said guide section spaced from the walls thereof by dielectric delay means arranged to impart a relative delay between said TEM, and TEO, modes of substantially 90 electrical degrees within said prescribed frequency range, land means between said dieleotric delay means and said rectangular opening for absorbing energy traveling from said horn toward said rectangular opening which would arrive thereat with its electric vector oriented generally parallel to said wide dimension while negligibly attenuating microwave energy travelling in the sarne direction and arriving at said opening with its electric vector oriented generally parallel to said narrow dimension.

3. A rotary waveguide joint comprising, a pair of transmission assemblies each having a horn closely adjacent to and facing the horn of the other `assembly for exchanging circularly polarized energy therebetween within a prescribed range of frequencies, a guide section formed with a rectangular opening lat one end and having a portion of square cross section coupled to said opening by a transition section arranged to accept energy incident at said opening having its electric vector substantially parallel to the narrow dimension of said opening `and deliver said energy to said square portion with its 4electric vector then oriented substantially parallel to one of lthe diagonals of said square cross section to establish TEM and TEM components of substantially equal magnitude within said square portion, the dimensions of said rectangular opening being selected to correspond to those of a rectangular waveguide capable of supporting the propagation of microwave energy within said prescribed range having its electric vector parallel to the narrow dimension of said opening while suppressing propagation of microwave energy Within said prescribed range having its electric vector parallel to the wide dimension of said opening, said portion of square cross section being dimensioned to support the propagation of both TEM, and TEM modes of microwave energy within said frequency range, a metallic insert within said guide section spaced from the Walls thereof by dielectric plates angularly displaced by substantially degrees about the axis of said section, respective pairs of said plates being generally parallel to the electric vectors of said TE, and said TEM components respectively to impart a relative delay between said TEN and T E01 components of substantially 90 electrical degrees within said prescribed frequency range to deliver circularly polarized energy to said horn, and plates of dissipa- -tive material within said section adjacent to said portion of square cross section in the plane passing through the axis of said sections including said other diagonal.

4. Apparatus for transmitting circularly polarized energy of a predetermined rotation over a prescribed frequency range comprising, a horn for receiving circularly polarized energy, a guide section formed with a rectangular opening at one end and having a portion of square cross section coupled to said opening by a transition section arranged to accept microwave energy incident at said opening having its electric vector substantially parallel to the narrow dimension of said opening and deliver said energy to said square portion with its electric vector then oriented substantially parallel to one of the diagonals of said square cross section, the dimensions of said rectangular opening being selected to correspond to those of a rectangular waveguide capable of supporting the propagation of energy within said prescribed frequency range having its electric vector parallel to the narrow dimension of said opening while being incapable of supporting propagation of energy within said prescribed range having its electric vector parallel to the wide dimension of said opening, said portion of square cross section being dimensioned to support propagation of both TEN and TEM modes of energy within said prescribed range, a metallic insert within said guide Lsection spaced from the walls thereof by dielectric plates angularly displacedby substantially 90 degrees about the axis of said section, respective pairs of said plates being generally parallel to the electric vectors of said TEM, and said TE01 modes respectively to impart a relative delay between the latter modes of substantially 90 electrical degrees within said prescribed frequency range to convert circularly polarized energy from said horn into linearly polarized energy, and plates of dissipative material within said section adjacent to said portion of square cross section in the plane passing through said axis including said other diagonal.

5. High frequency apparatus comprising, a first wave transmission conduit capable of delivering linearly polarized high frequeppy energy over a prescribed frequency range polarized in a first direction through an opening in said conduit to an external wave transmission conduit while linearly polarized energy travelling toward said opening and polarized normal to said first direction will be reected back into said iirst conduit, a second wave transmission conduit connected to said first conduit and capable of propagating both orthogonal components of crossed linearly polarized energy within said prescribed range polarized along said first direction, means within said second conduit for imparting a relative phase delay of substantially 90 electrical degrees between said first and second orthogonal components, and a dissipative sheet within at least one of said first and second conduits in a plane normal to said first direction for suppressing the propagation of crossed linearly polarized energy polarized along a direction orthogonal to said rst direction while allowing energy polarized along said first direction to propagate with negligible attenuation toward said opening.

References Cited in the file of this patent UNITED STATES PATENTS 21,526,383 Meier Oct. 17, 1950 2,535,251 Alford Dec. 26, 1950 2,649,578 Albersheim Aug. 18, 1953 2,713,151 Farr July 12, 1955 2,741,744 Driscoll Apr. 10, 1956 

